The present invention concerns monolithic substrates for electronic power components. Such substrates are formed by a sintered stack of layers of dielectric material, generally a ceramic, or an alumina for hyperfrequency applications.
Such substrates can be used both for carrying semiconductor devices at a high density (they are then known as a chip carrier), or as substrates which are intended for producing hybrid circuits, using a procedure which is conventional in itself. In both cases, the substrates are often interconnection substrates, that is to say they include integrated conducting connections (which are buried in the substrate or formed at the surface thereof) which will subsequently be connected to terminals of the component. Such interconnections are often distributed over a plurality of layers, wherein interconnections from one layer to another and to the surface of the substrate are incorporated in accordance with a predetermined layout.
By virtue of the high density of the components, or when there is a wish to use power components (amplifiers in a hybrid circuit for example), it becomes necessary to absorb and dissipate a substantial amount of heat which is given off by the components. By way of example, it is often necessary to dissipate an amount of power of the order of 35 watts by means of a substrate of standardized dimensions of 152.4.times.86.36 mm.
For that purpose, the material generally chosen for the substrate is a material which is a good conductor of heat such as alumina which also has excellent dielectric and mechanical properties. That choice is important in particular when very strong currents pass through the buried interconnections, in order to drain the heat produced in the center of the substrate towards the surface thereof.
In order to dissipate the heat which is drained away in this manner, a first method contemplates using metallic radiators which are glued to the back of the substrate, the heat being discharged by conduction through the mass of the radiator and then by natural or forced convection to the ambient atmosphere.
Another procedure which can be used in combination with that described above comprises providing, in the center of the substrate, metallization portions which act as heat sinks and which open onto a face of the substrate by way of studs which are then welded to a metal chassis made, for example, of copper or Duralumin.
However those two methods suffer from the disadvantages that they occupy a complete face of the substrate which is therefore no longer available for carrying components, they necessitate substantial metal masses in order to remove the heat produced by conduction and convection, and finally, for that eason, they limit the options in regard to physical arrangements of the substrate and the components within the piece of equipment.
At any event, the possibility of in situ absorption of the heat produced is limited by virtue of the interposition of an intermediate member, a heat sink or a radiator.